proud



Jan. 21, 1964 R. A. PROUD, JR

PHOTOGRAPHIC TYPE COMPOSITION Original Filed Sept. 29, 1959 2Sheets-Sheet 1 IN VEN TOR.

ATTORNEYS Jan. 21, 1964 R. A. PROUD, JR

PHOTOGRAPHIC TYPE COMPOSITION Original Filed Sept. 29, 1959 2 sheetssheet 2 FIG-5 INVENTOR RALPH A Pmwmn ATTORNEYS United States Patent 2Claims. (Cl. 95-45) This invention relates to phototypesettingapparatus, particularly to an improved optical system forphototypesetting machines providing for rapid, accurate, and easyadjustment of the point size of the individual characters reproduced.

In accordance with this invention the optical system includes simple andinexpensive lenses, as of the ordinary double-convex type, andadjustable mountings for each lens are provided for relative movement ofeach lens with respect to the others. The mountings are supportedadjacent the type matrix of the phototypesetting machine, on theopposite side thereof from a flash source of light which is controlledto illuminate a selected one of the characters on the matrix and thusproduce an image bearing light beam. The lenses transmit such beam tophotosensitive material which is mounted at a fixed distance from thematrix, defining an optical system in which the image to object distanceis a constant. With proper maniplation of the lenses the magnificationof the character image focused on the record material may be adjusted asdesired within the limits of the system.

In high-spced phototypesetting systems a high intensity short durationlight source, such as a spark gap or a gas discharge tube, is needed forhigh-speed photography. To obtain long life from such a source it isdesirable to keep the energy of each discharge to a minimum, and sincethe time-light product of the source is a function of the energy in thedischarge, an optical system of high efficiency is necessary. An opticalsystem which produces sharp images with a relatively wide lens apertureis necessary to accommodate the range of sizes desired. The presentinvention provides such a system.

Basically, an optical system in accordance with the present inventionmay be provided by two simple lenses each having adjustable mountings,together with a coordinated adjustment system which positions each lensaccurately in different relative positions according to the desired sizechange from a basic object member, which may for example be on acharacter matrix plate or the like. With such a system, using characterobjects of approximately eleven point size, and with the two lensesoperating as a composite lens, with no real image formed therebetween,it is possible to obtain a range of character image sizes from aboutthree and one-half to approximately forty points.

However, in many applications it may be desirable for the machine toproduce substantially larger character images, while operating from thesame basic eleven point objects. In such case, the two lenses may bepositioned differently, with a real image formed between them, or amodified optical system may be provided in accordance with the inventioncapable of producing character images up to at least seventy-two points.Such a modified optical system may be considered as comprising twoseparate image forming lens groups. Each group essentially includes twolenses, and the two lenses nearest the character matrix are henceforthcalled the main lenses, operating as a variable composite lens, and thetwo lenses nearest the image will be called the auxiliary lenses. Of theauxiliary lenses, the one nearer the image plane (photosensitive recordmaterial) will be referred to as the magnifier or multiplier and theother will be called the field lens.

The use of four lenses in the system provides a much larger range ofimage sizes, as noted above, and for this purpose the auxiliary lensesare used to provide gross steps of magnification such as 1:1, 2:1, or4:1. To form an image upon the record material these auxiliary lensesact upon the light from the image formed by the main lenses in the samemanner as the main lenses act upon the light from the character matrix.Therefore, with such a main and auxiliary arrangement it is possible touse the adjustments in the main system through one range of settings ofthe auxiliary system, then to change the gross step by altering thesetting of the auxiliary lenses and again utilizing essentially the samesettings of the main system to provide a further range of settingswithin the next gross step of magnification.

Accordingly, the primary object of this invention is to provide animproved and highly efficient optical system for phototypesettingapparatus, which system is relatively inexpensive and easy tomanufacture, and which includes easily operated controls for adjustingthe system to produce character images of a selected point size.

Another object of the invention is to provide such an 4 optical systemfor phototypsetting apparatus wherein two simple lenses are arranged forrelative movement with respect to each other, and the type matrix andthe photosensitive record material are supported in fixed spacedrelation on opposite sides of the two lenses, and wherein a real imageis formed between the two lenses in all positions thereof at whichdifferent sized objects of type material are focused on the recordmaterial.

Another object of the invention is to provide an improved optical sizecontrolling system for phototypesetting machines which, whilemaintaining a fixed image to object distance, incorporates main andauxiliary lens systems, for example two independently movable lenseseach, wherein the auxiliary lenses are positioned independently of themain lens system to provide gross steps of magnification resulting inlarge point size character images which it is impossible to attainthrough the basic two lens system.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

This application is a division of application Serial No. 843,127, filedSeptember 29, 1959, and assigned to the same assignee as thisapplication.

In the drawings- FIG. 1 is a schematic plan view of an optical systemand associated control as provided in accordance with the invention;

FIG. 2 is a view taken along line 22 in FIG. 1;

FIG. 3 is an enlarged end view in elevation, of one of the rotary stopcylinders shown in FIGS. 1 and 2;

FIG. 4 is a developed view of the stop cylinder shown in FIG. 3,illustrating the relative positions of the various stops on dilferentsegments of the stepped end surface thereof;

FIG. 5 is a schematic plan view similar to FIG. 1 showing the modifiedoptical system incorporating main and auxiliary lens groups;

FIG. 6 is a diagram showing one method of locating the character fieldwith respect to the axis of the optical system, providing for properalignment of the starting or left hand edge of the character field inspite of changes in size of the character image;

FIG. 7 is a view similar to FIG. 6 showing a modified arrangement of thecharacter field with respect to the axis of the optical system; and

FIG. 8 is a diagram of a margin adjustment apparatus which would beutilized with the system shown in FIG. 7.

Referring to the drawings, which illustrates a preferred embodiment ofthe present invention, the optical system provided by this invention andassociated parts of a typical phototypesetting machine are shown asincluding a type matrix it} which may be in any suitable form, such forexample as a continuously rotating disk such as shown and described inthe 'copending application Serial No. 380,802, filed September 17, 1953,now United States Patent No. 2,846,932, which is assigned to the sameassignee as this application. The characters on this disk comprise partsof differential light transmitting ability, for example, the characterparts being transparent and the background opaque. A selectivelyoperable light source of high intensity and short duration is provided,for example by a pair of spaced electrodes indicated generally at 12 andoperable by a suitable control 13 which impresses a high voltagepotential difference across the electrodes to produce the desired highintensity spark or flash of light at the instant when a selectedcharacter on matrix passes the light source. The resultant characterimage bearing light beam is directed through the optical system to asuitable spacing prism. arrangement indicated generally at "15, andwhich may be for example the type shown in the copending applicationSerial No. 661,633, filed May 27, 1957, now United States Patent No.2,966,835 from which the light beam is directed in properly spacedrelation with respect to the preceding light beam upon a strip ofphotosensitive material or film 16.

The optical system includes a pair of lenses and 2 2, each of whichpreferably is of the ordinary positive double convex type, and eachsupported in a conventional housing, 24) and 22', respectively. Theselenses are mounted along the center line of the path between matrix disk1% and the spacing mechanism 15, defining an optical axis 23 whichextends through the center of each of the lenses. Lens housing 20' is.mounted on a suitable carrier 25 by an extension arm 26, and carrier 25is supported in sliding relation upon a track member 28 having a stop 29at its forward end, and extending parallel to the optical axis 23. Astop arm 30 projects from one side of carrier 25 for engagement with aplunality of selectively operable stops, and a spring 32 is connected atone end to carrier 25 and anchored at a fixed point at its other end 33so as to urge the carrier against a selected stop.

The selectively operable stop mechanism is provided by cylinder 35carried on a rotatably mounted shaft 36, and having a plurality of steps37ah formed along one end thereof in a generally helical pattern, eachstep carrying an associated adjustable stop pin 38ah which may bethreaded or otherwise adjustably fixed with respect to a step in the endof the stop cylinder.

The development of a suitable stop: cylinder is shown in FIG. 4, whereinthe progression of the stops with respect to the end of the cylinder andthe adjustment of the individual stop pins is readily apparent. Shaft 36is fixed to a sprocket 4t and a suitable lock pin 42 operated by asolenoid 43 is arranged for projection into suitable apertures (notshown) within sprocket 41? for retaining the stop mechanism at a chosenposition.

The other lens housing 22 is mounted on a carrier 45 by a supporting arm46, and carrier 45 is carried upon a track 43 having a stop 49 at itsforward end. In the same manner as previously described, stop 5i)projects from one side of carrier 45 for engagement with selectivelyoperated stop means, and a spring 52 is connected at one end to carrier45 and fixed at its other end. 53 for urging this carnier intoengagement with the stop means.

The stop means for carrier 45 is provided by a further stop cylinder 55mounted on a shaft 56 the rotation of which is controlled by a sprocket5'7. The details of stop cylinder 55 are exactly the same as thosedescribed above in connection with stop cylinder 35. A crank 4 arm 58extends from sprocket 57 for rotation thereof, and a chain 60 connectsthe sprockets 4t and 57 to coordinate rotation thereof in response torotation of crank 58, thereby providing a preselected setting of thestop cylinders 35 and 55 when the crank 58 is moved to a given angularposition.

A drive chain is connected at its opposite ends to carrier 45 and islooped around an idler sprocket 66 and a suitable drive sprocket 68 isconnected through a suitable slip clutch 69 to a shaft 76 driven by asmall electric motor 72 or other suitable driving means. Thus, whenmotor 72 is energized to rotate shaft '70 in a clockwise direction, asviewed in FIG. 2, lens carrier 45 will be moved forward toward the stop49.

As lens 22 moves forward its housing engages the housing of lens 20,advancing carrier 25 to engage with its stop 29, at which time clutch 69will slip. With the two carriers in a forward position and solenoid pin42 retracted, crank 58 can be rotated to set the stop cylinders 35 and55. Then, with the stops set as desired the control may be deenergizedand the springs 32 and will retract the lens carriers into engagementwith their respective selected stop pins. It will be apparent that inthis manner the location of each of the lenses 29 and 22 with respect tomatrix ltl can be adjusted, and at the same time the distance betweenthe two lenses preselecte The optical system has a fixed object, thechosen character on matrix it and the object to image distance remainsconstant since there is no movement of the record strip 16 away from thematrix it Therefore, for given positions of the two lenses there will bean image focused on record strip 16 which is magnified in accordancewith known optical relationships as follows.

In any optical system where F is the focal length, i is the imagedistance, and 0 is the object distance,

I I 1 F Z 5 and where m is the magnification (2) 0=mi Substituting (2)in (1) yields I I I and solving for i gives 4 i: m Substituting (2) in(4) yields (5 0=F(m+1) and adding (4) and (5) gives In a two lens systemthe relationship between the focal length of each lens is expressed asfollows, where i equaas the distance between the two lenses,

Then assuming that f equals f (7) can be reduced" and terms combined togive Equation (8) may then be substituted in (6) to yield By crossmultiplying (9) gives and solving (1) for I gives 1 (1L) m(i+)Considering Equation 11, and recalling that in the phototypesettingapparatus the image to object distance (id-0) is a constant, andrealizing that the focal lengths of lenses 2% and 22, will be a constantonce chosen, it will be appreciated that variations in magnification mcan be accomplished with appropriate changes in the separation distancer. Thus, any given setting of stop cylinders 35 and 55 will result in agiven selected separation of the lenses 2t and 2 2 and the desiredmagnification of the character image focused on film 16.

The foregoing equaltions and explanation assume that the two lenses areoperating as a composite variable power lens in wnich no real image isformed between the lenses. it is also possible to have a two lens systemin which an image to object distance D is fixed and a real image isallowed to form between the lenses, while achieving variablemagnification of the obiect. The total magnification of the system isequal to the product of the magnification m of the first lens L and themagnification m of the second lens L i.e., Mm m Assuming the followinggeometrical proportions, the explanation of the system will be apparent.Let D equal the distance between the object (character) plane and tneimage (record material) plane which for a system of the type hereinconcerned will be a constant. The distance from the object to L will beequal to a. The distance from L to the first real image 1 between thelenses L and L will equal 1). The distance from T to L will equal 0, andthe distance from L to the record plane image I will equal d.

Fundamental lens equations show that f1 (1 b where f is the focal lengthof lens L it follows that b m and since it follows that the first image1 will be an inverted real image formed at a distance of n+1) from theobject, and therefore a b =f and therefore in ft 641-11 al-ba+f f if ais less than or equal to h, no real image I, would be formed.

The second lens L must work within the remaining distance c+d to form animage upon the record plane. Therefore,

as determined by the magnification m afforded by lens L Thus, thedistance a when f f and D are fixed, as they are in typical embodimentsof the invention, will determine the distance d and the magnification mof lens L as follows.

The last above equation is a quadratic equation in a, and thereforethere are two possible values of a for each value of d, or converselytwo values of d for each value of a. Accordingly, there are two valuesof final magnification M for each usable value of a in a working systemof the type above described.

In coordinating and calibrating the settings of the stop cylinders andeach of the associated stop pins, the magnification of the characterimage may thus be related to a given point size of type, in measurementsfamilar to the printer, and the angular positions of crank 58 may berelated to different point sizes. A suitable indicator (not shown) maythen be associated with the crank and the operator may procure a desiredpoint size merely by pressing switch button 75 to release lock pin 42and start motor 72. This frees the optical system for setting the crank58 accordingly. When the switch button is released the springs 32 and532 will return the carriers to be stopped at their respective newlyselected positions.

As will be apparent from an inspection of FIG. 1 of the drawing theoptical system of this invention may be, in practical use, of relativelyshort length. This is advantageous from the standpoint that thecharacter images may be sharply and accurately focused upon thephotosensitive record material, thereby providing a high quality recordwhich is necessary, for instance, in preparing a galley for use inphotolithography or the like.

Furthermore, the accuracy of the system depends, in the case of eachpoint size, upon the final or fine adjustment of the individual stops3Sah, and thus location of the rotating stop cylinders 35 and 55, onceestablished, does not further effect the optical system. Adjustment ofthe system by rotation of these cylinders has no effect upon the properfocusing of the images in any given point size, since any slightdeviation due to non-parallel mounting between the optical axis and theaxes of rotation of the stop cylinders may be compensated for by fineadjustment of the individual stops.

Referring to FIG. 5, a modified system in accordance With the inventionis illustrated, with like reference numerals in the series indicatingidentical or functionally similar parts as described in connection withFIG. 1. In this system, in addition to the main lens system comprisingthe lenses 29 and 2.2, there is also an auxiliary lens system comprisingtwo lenses 1% and 182, mounted in housings 183 and 13%, respectively.The lens 182, closer to the record material 116 and the image plane, isdesignated the magnifier or multiplier lens, and the lens 189 is termedthe field lens. The use of this additional lens system provides forcoverage of a larger range of image sizes in combination with a two lenssystem where an image is not formed between the lens. The auxiliarylenses are used to provide gross steps of magnification, and forpurposes of explanation herein it will be assumed that these lensesoccupy alternately each one of two different positions,

The lens housing 183 is mounted on a carrier 186 which in turn slidesupon a rod or track member 187,

and stop collars or the like 12 2 are provided for motive doubledefining alternate positions of lens 1%, with the power for changingpositions being supplied by a acting pneumatic motor, or the lilte,which has its. output piston rod 195 coupled to carrier 11% as shown,.and which is controlled by a sevo valve operated by solenoid 15 7. Themagnifier lens 132 is likewise posi-- tioned through its carrier 2%mounted on track 2% and movable between stop collars 2% and undercontrol. of a fluid motor 265 which has its output 296 coupled to thecarrier 2%. The motor 2%.? is in turn operated by servo valve 214controlled by he solenoid 212. in the position shown the auxiliarylenses are positioned for lzl magnification, or in other words, theyhave essentially no size controllin: effect upon the images passedtherethrough. By moving these lenses to their alternate positions,against the respective stops 3'92 and a gross multiplication ormagnification may be obtained as desired, for example magnifying allimages passed therethrough by a ratio of 4:1. incremental changes inimage size within the 4:1 range may be accomplished by furtheradjustment of the lenses in the main system.

Coordination between the two systems is provided by a cam 215 on drumshaft 156, opera-ting to close 21 normally open switch 22% and toenergize solenoids 1?? and .212 to provide for shifting of the auxiliarylenses to their 4: 1 position as the main lense system, and the controldrums therefor, are rotated through a predetermined angular extent. Itwill be appreciated, of course, that the array of stops on the controldrums 135 and 155 may necessarily be in different sequence than thatshown for example in FIG. 4, since the main lenses may occupy the sameposition twice while providing different ultimate magnifications incombination with the auxiliary lens system.

The resetting motor for the main lens system may also be of somewhatdifferent construction, including a singleacting fiuid motor 165 havingan output piston 3 .67 coupled to the carriage 145. The supply ofpressure fluid from a suitable source P is controlled by a solenoidoperated valve 176 having an operating solenoid 172 which is energizedwhen the manual switch M is closed, to pass pressure fluid to the motor.In the same manner as previously described in connection with FIG. 1,closing of this switch also energizes the lock solenoid 143 to withdrawthe lock pin 142 and permit resetting of the control drums 155 and 1355by rotation of the crank handle 158.

The motor 165 operates in the same manner, withdrawing the carriage 145to the top, as viewed in PEG. 5, against spring 152 until the housing17:22 engages housing 129, after which the carriage 125 is alsowithdrawn to its base position, defined by stop 129. When the solenoid172 is subsequently deenergized the motor 165 will be vented toatmosphere through valve 170, in accordance with usual practice,permitting the springs 132 and 152. to advance their correspondingcarriages to engage the stops on the control drums at their newsettings.

Referring to FIG. 6, the relation between the character field, withinwhich all character images are projected, and the lenses of the opticalsystem, is illustrated. For purposes of explanation, it will be assumedthat the lens 226 in FIG. 6 corresponds for example to the lenses 2 h or12d in PlGS. 1 and 5. The optical axes XX and Y[ extend through thecenter of the lens, and the left edge of the character field, indicatedby the dot-dash line 222 coincides with the YY axis. "i" to upper case Wis used as an illustration, since this character is one of the lar estin a font, and occupies essentially the entire upper portion of thefield, with the lower edge of the character on e X-X axis.

The bottom line 224- of the character field is somewhat below the XXaxis, to accommodate the descenders of certain characters, particularlythe lower case y, p and g. It will be apparent from the drawing that thecharacter field occupies essentially one quadrant of the optical system,with the exception that the descenders above noted extend into thesecond quadrant. As the lenses are located in different positions, inaccordance with any of the mechanisms previously described, the leftmarginal line 222 of the character field will always remain coincidentwith the vertical or YY axis of the lens system, and the characterimages appearing in the final image plane (i.e., on the reproductionmaterial) will always begin on the some left hand or reference line.Thus, particularly with re 'ard to the first character in a line ofcomposition, the characters will always be properly aligned with theleft hand margin no matter what optical change may be effected toproduce relatively large or smaller character images.

FIGS. 7 and 8 show a modified arrangement of the character field withreference to the optical system. In this arrangement the optical axesXl-Xll and Y 1-3 1 intersect at the center of a lens 230, and thecharacter hold is arranged within the optical system having its verticalcenter line 232 coincident with the Yll-Yl axis. Therefore, in the caseof the upper case W shown, the character will be centered in the uppertwo quadrants of the system, and descenders would project somewhat intothe lower two quadrants. The base of the character will coincide withthe Xl-Xl axis, with the descenders projecting therebelow. This ystempermits the use of smaller lenses, but all character images will becentered on the Yl"l axis, and thus the left edge of the character fieldmay be of variable position in the final image plane, depending upon theoptical size change produced by the system.

With such a system, it is therefore necessary to adjust the leftmarginal edge of the character field in accordance with optical changesto maintain coincidence of the left hand margin of the character fieldin composing different lines and using different size images. A suitablesystem for this purpose is shown in FIG. 8, wherein the record material236 may be advanced through large increments, to perform large spacingmovements during composition of a line, and where a movable prism 237,or a similar suitable movable reflecting or other member for changingthe optical path through small increments, may be variably positionedunder the control of a transducer 24% capable of producing smallincremental movements within the range between the large movementincrements of the record surface 236. One suitable transducer for thispurpose is shown in Patent 2,889,108, issued June 2, 1959, and assignedto the assigns of this application.

The aforementioned adjustment of the character field to accommodatedifferent optical changes (in a system such as shown in FIG. 7) isaccomplished by another variably movable prism 242 (or a suitableequivalent) which is capable of assuming a number of differentincremental positions with reference to the longitudinal optical axis24d of the lens system, thereby varying the location of the characterimage as it passes through the small increment spacer 237. The member2-4-2 may lil ewise be under the control of a transducer havingessentially the same construction as the transducer and controlled inany suitable manner to produce the necessary adjustment in the member 2While the forms of apparatus herein described constitute preferredembodiments of the invention, it is to be understood that the inventionis not limited to these precise forms of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. In phototypesetting apparatus having a matrix carrying a plurality ofcharacters, a selectively operable device providing a flash source oflight having relatively high intensity and relative short duration,means supporting said matrix adjacent said light source to illuminatethe characters individually in selected sequence and to producesuccessive light beams bearing images of the selected characters, meansconducting said light beams along a common predetermined path, means forsupporting a photosensitive record material on said path in an imageplane at a fixed distance from said matrix for recording of thecharacter images thereon, a pair of lenses, individual carriers for eachor" said lenses supporting said lenses in spaced relation along saidpath between said matrix and said record supporting means, meansdefining paths of movement for each of said carriers parallel to saidpath of said light beams, selectively operable stop means for each ofsaid carriers cooperating therewith to position said carriers at aplurality of locations along their respective paths of movement, andcoordinating control means operative on said stop means to selectcombinations of settings of said stop means corresponding topredetermined different separations of said lenses at which difierentsizes or" character images are produced and in each setting or which areal image is formed between said lenses.

2. In phototypesetting apparatus of the character described an opticalsystem comprising, a selectively operable device providing a lightsource a matrix having a plurality of character objects as portions ofdifferential light transmitting ability, means mounting said lightsource adjacent said matrix for illuminating a selected one of saidcharacters, a photosensitive record material, means supporting saidrecord material in an image plane at a fixed distance from said matrixto record the image resulting from illumination of a character, a pairof lenses arranged in spaced relation between said matrix and said.record material defining a main optical size control system, a fieldlense and a multiplier lense arranged serially and receiving all the thelight passed through said main optical system, movable carriers for eachof said lenses, means defining independent paths of movement for each ofsaid carriers for focusing real images of variable magnification withrespect to the character objects upon said record material, meansincluding a plurality of selectively operable stops engageable with thecarriers of said main system for positioning main system carriers atpreselected locations corresponding to the obtaining of real images ofdesired point sizes on said record material, means operative to positionsaid carriers tor said field and multiplier lenses to provide grosssteps of image size control, and control means operable from a singlelocation for positioning said lenses at locations (orrespondto a desiredpoint size.

No references cit-ed.

1. IN PHOTOTYPESETTING APPARATUS HAVING A MATRIX CARRYING A PLURALITY OFCHARACTERS, A SELECTIVELY OPERABLE DEVICE PROVIDING A FLASH SOURCE OFLIGHT HAVING RELATIVELY HIGH INTENSITY AND RELATIVE SHORT DURATION,MEANS SUPPORTING SAID MATRIX ADJACENT SAID LIGHT SOURCE TO ILLUMINATETHE CHARACTERS INDIVIDUALLY IN SELECTED SEQUENCE AND TO PRODUCESUCCESSIVE LIGHT BEAMS BEARING IMAGES OF THE SELECTED CHARACTERS, MEANSCONDUCTING SAID LIGHT BEAMS ALONG A COMMON PREDETERMINED PATH, MEANS FORSUPPORTING A PHOTOSENSITIVE RECORD MATERIAL ON SAID PATH IN AN IMAGEPLANE AT A FIXED DISTANCE FROM SAID MATRIX FOR RECORDING OF THECHARACTER IMAGES THEREON, A PAIR OF LENSES, INDIVIDUAL CARRIERS FOR EACHOF SAID LENSES SUPPORTING SAID LENSES IN SPACED RELATION ALONG SAID PATHBETWEEN SAID MATRIX AND SAID RECORD SUPPORTING MEANS, MEANS DEFININGPATHS OF MOVEMENT FOR EACH OF SAID CARRIERS PARALLEL TO SAID PATH OFSAID LIGHT BEAMS, SELECTIVELY OPERABLE STOP MEANS FOR EACH OF SAIDCARRIERS COOPERATING THEREWITH TO POSITION SAID CARRIERS AT A PLURALITYOF LOCATIONS ALONG THEIR RESPECTIVE PATHS OF MOVEMENT, AND COORDINATINGCONTROL MEANS OPERATIVE ON SAID STOP MEANS TO SELECT COMBINATIONS OFSETTINGS OF SAID STOP MEANS CORRESPONDING TO PREDETERMINED DIFFERENTSEPARATIONS OF SAID LENSES AT WHICH DIFFERENT SIZES OF CHARACTER IMAGESARE PRODUCED AND IN EACH SETTING OF WHICH A REAL IMAGE IS FORMED BETWEENSAID LENSES.